import React, { Component } from 'react'

export default class Count extends Component {

    state = { count: 0 }

    //加法
    increment = () => {
        const { value } = this.selectNumber;
        const { count } = this.state;
        this.setState({ count: count + parseInt(value) });
    }

    //减法
    decrement = () => {
        const { value } = this.selectNumber;
        const { count } = this.state;
        this.setState({ count: count - parseInt(value) });

    }

    //奇数再加
    incrementIfOdd = () => {
        const { value } = this.selectNumber;
        const { count } = this.state;
        if (count % 2 !== 0) this.setState({ count: count + parseInt(value) });
    }

    incrementAsnyc = () => {
        const { value } = this.selectNumber;
        const { count } = this.state;
        setTimeout(() => { this.setState({ count: count + parseInt(value) }) }, 500);
    }

    render() {
        return (
            <div>
                <h1>当前求和为: {this.state.count}</h1>
                <select ref={c => this.selectNumber = c}>
                    <option value='1'>1</option>
                    <option value='2'>2</option>
                    <option value='3'>3</option>

                </select>&nbsp;
                <button onClick={this.increment}>+</button>
                <button onClick={this.decrement}>-</button>
                <button onClick={this.incrementIfOdd}>当前求和为奇数再加</button>
                <button onClick={this.incrementAsnyc}>异步加</button>
            </div>
        )
    }
}
